import java.util.*;

public class Main {
    // 养兔子
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long[] res = new long[91];
        res[1] = 1;
        res[2] = 2;
        for (int i = 3; i < res.length; i++) {
            res[i] = res[i-2] + res[i-1];
        }
        while (in.hasNextInt()) {
            int n = in.nextInt();
            System.out.println(res[n]);
        }
    }



    // 收件人列表
    public static void main3(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNextInt()) {
            StringBuilder builder = new StringBuilder();

            int n = in.nextInt();
            in.nextLine();
            String[] strings = new String[n];
            for (int i = 0; i < n; i++) {
                strings[i] = in.nextLine();
            }
            for (int i = 0; i < strings.length; i++) {
                if (strings[i].contains(" ") || strings[i].contains(",")) {
                    if (i == strings.length-1) {
                        builder.append("\"").append(strings[i]).append("\"");
                        break;
                    }
                    builder.append("\"").append(strings[i]).append("\"").append(", ");
                    continue;
                }
                if (i == strings.length-1) {
                    builder.append(strings[i]);
                    break;
                }
                builder.append(strings[i]).append(", ");
            }
            System.out.println(builder);
        }
    }


    // 客似云来
    public static void main2(String[] args) {
        Scanner in = new Scanner(System.in);
        long[] arr = new long[81];
        arr[1] = 1;
        arr[2] = 1;
        for (int i = 3; i < arr.length; i++) {
            arr[i] = arr[i-2] + arr[i-1];
        }
        while (in.hasNextInt()) {
            int from = in.nextInt();
            int to = in.nextInt();
            long res = 0;
            for (int i = from; i <= to; i++) {
                res += arr[i];
            }
            System.out.println(res);
        }
    }


    // 剪花布条
    public static void main1(String[] args) {
        Scanner in = new Scanner(System.in);
        while (in.hasNext()) {
            String s1 = in.next();
            String s2 = in.next();

            int count = 0;
            while (s1.contains(s2)) {
                count++;
                s1 = s1.replaceFirst(s2, "");
            }
            System.out.println(count);
        }
    }
}
